1. Field of the Invention
The present invention relates to a color cathode ray tube, and more particularly, to a mask in a color cathode ray tube for selecting colors of electron beams.
2. Background of the Invention
Of the color cathode ray tubes currently available, related art flat cathode ray tubes are spreading widely. These will be explained briefly.
Referring to FIG. 1, the related art flat color cathode ray tube is provided with a flat panel 1 of glass, and a funnel 3 in a form of a bulb welded to a back surface of the panel 1 by using Frit glass, to form an enclosure, with an inside space at a 10xe2x88x927 Torr high vacuum. There is a safety glass 5 attached to a front surface of the panel 1 by using resin for prevention of explosion of the cathode ray tube, and R, G, B fluorescent film 2 coated on an effective area of a back surface of the panel 1 in a fixed pattern. There is a rail assembly 7 of rectangular metal frame bonded to a non-effective area of the panel 1 by using Frit glass, and a mask 11 welded to the rail assembly 7 having a fine beam pass through holes 10 of slit or crevice form at fixed intervals for selective passing of the R, G, B electron beams 9. There is an electron gun 13 sealed in a bottle-neck formed neck portion 4 in a rear portion of the funnel 3 for emission of electron beams 9, and a yoke 15 on an outer circumference of the neck portion 4 for forming vertical and horizontal magnetic fields to deflect and direct the electron beams 9 to an entire surface of the panel 1.
When power is provided to the foregoing flat cathode ray tube through a plurality of stem pins 16 at a rear portion thereof, thermal electrons(electron beams) are emitted from the cathodes as a heater in the electron gun 13 is heated, controlled, accelerated and focused as the electron beams 9 pass through a plurality of electrodes in the electron gun 9 in succession, subjected to color selection as the electron beams 9 pass through the mask 11 on an electron beam travel path, and collides onto the fluorescent film 2 coated on an inside surface of the panel 1. A picture is formed as the electron beams 9 are deflected by the yoke 15 on the outer circumference of the neck portion 4 to the screen area.
In the meantime, referring to FIGS. 2 and 3, only 20-25% of the electron beams 9 from the electron gun 13 pass through the beam pass through hole 10 in the mask 11, while approx. 75-80% is cut off at the non-hole portion 12. The electron beams 9 cut off at the mask 11 are converted into thermal energy, to expand the mask 11 by the thermal energy, thereby causing doming in which the path of the electron beams incident to the screen is changed, to thereby deteriorate color purity. Consequently, to prevent the doming of the mask 11, a tension mask is employed, wherein the tension mask is strained before it is fixed to the rail assembly 7 so that the tension mask can counteract the thermal expansion. In order to strain the tension mask, it is not only required to have an appropriate material property, but also an appropriate thickness, which is in a range of 25xcx9c80 xcexcm. However, even if the mask 11 has a thickness within the above range, it is required to be subjected to rolling 1 or 2 times for flattening, which delays fabrication and pushes up costs. The mask 11 is liable to plastic deformation, such as crumpling, bending, tearing off, or other damage, which deteriorate productivity. For fear of deformation, the mask 11 cannot be subjected to a washing process for removing foreign matter stuck to it, which causes foreign matter to lodge in the beam pass through holes 10. Another problem of occurrence of howling in which the picture looks wavy as the electron beams collide, and the color on the screen is abnormal owing to vibration of the mask 11 that is caused by even a small external impact. As a solution for this, the thickness of the mask 11 is designed to be approximately 80 xcexcm (an allowable maximum range of tension thickness) as shown in FIG. 3. However, the above solution causes other problems. Particularly, the thicker mask 11 also forms a thicker wall of the beam pass through hole 10, that deteriorates transmissivity of the electron beams 9. That is, as shown in FIGS. 4 and 5, if the two masks 11 are compared to be t1 less than T1, wall tapers of the beam pass through holes 10 are also compared to be t2 less than T2, and, accordingly, bridge areas formed between each beam pass through holes 10 in a width direction are also compared to be s3 less than S3. Consequently, the increased bridge surface increases a cut off amount of the electron beams 9, that reduces the transmissivity of the electron beams, and deteriorates luminance.
Accordingly, the present invention is directed to a mask in a color cathode ray tube that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a mask in a color cathode ray tube, in which a structure of the mask is improved for reducing howling and doming and improving luminance.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the mask in a color cathode ray tube, including electron beam pass through holes with bridges connected to non-hole portions between the beam pass through holes in a width direction, wherein a thickness of the bridge of the mask facing an electron gun is formed thinner than other portions of the mask, thereby attenuating howling and enhancing luminance.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.